Tris organo sulfonium salts is an important class of sulfur compounds. Sulfonium salts have received renewed interest since the discovery that some triaryl sulfonium salts could be utilized as latent initiators for cationic polymerization, as disclosed in U.S. Pat. Nos. 4,058,400 and 4,058,401. These salts were activated photochemically. More recently, it has been found that some benzylic sulfonium salts can be utilized as latent thermal initiators for cationic polymerization, see for example PCT-application SE 90/00179 (23 Mars 1989); U.S. Pat. No. 5,013,814 (16 Jan. 1989); Japan-patent no. JP 63,221,111 (11 Mars 1987) Chem. Abstr. 1989, 111, 40092; Endo. T and Uno, H. J. Polym. Sci., Polym. Lett. Ed. 1985, 23,359; Pappas S. P. and Hill. L. W. J. Coat. Technol. 1981, 53, 43.
The latter have been shown to be thermally labile and decompose upon heating, leading to heterolytic cleavage of a sulfur-carbon bond yielding a sulfide and a carbocation capable of initiating the cationic polymerization. It has also been shown that the propagation rate of the cationic polymerization is very much dependent of the nature of the anion and as a result it is necessary that the sulfonium salt initiator has a non-nucleophilic anion X.sup.-, e.g. SbF.sub.6.sup.-, PF.sub.6.sup.-, AsF.sub.6.sup.-, and BF.sub.4.sup.-, as disclosed in U.S. Pat. Nos. 4,058,400 and 4,058,401. J. Appl. Polymer Sci. 1978, 43, 4826 and Makromol. Chem. 1985. 136.